This is a 20mm modification of a Enclosed Cable Carrier by Landru. I added two end parts and opened up the links to be able to get the cable in when the chain is in place. Put the links every other left and every other right. :)
Update: Replaced the skp file with a new one also containing smaller version of the closed link and end parts.
Scale to whatever you want, print and use. I have scaled down the link to less then 10mm over the "beam" and it still works good. :)